Known security detection systems are used at travel checkpoints to inspect carry-on and/or checked bags for concealed weapons, narcotics, and/or explosives. At least some known security detection systems include X-ray imaging systems. In an X-ray imaging system, an X-ray source transmits X-rays through a container, for example a suitcase, towards a detector, and the detector output is processed to identify a set of objects and/or materials in the container.
At least some known security detection systems utilize “Advanced Technology” (AT) scanners for multiview transmission imaging. Such known security detection systems view a container from two or three X-ray source perspectives. The resulting projection images may be compared to model projection images of hypothetical container contents, such as clothes, hygiene articles, books, or other common objects, to allow objects in the container to be recognized. In at least some known security detection systems, the multiview projections also may be combined using tomosynthesis or “limited angle reconstruction” to derive section images of the container. The use of each, or a combination, of these techniques for processing stereoscopic information provides enhanced detection of threats relative to single perspective X-ray screening machines. However, an amount of information about the contents of a container that can be derived from multiview transmission imaging using only two or three X-ray source perspectives is disadvantageously limited.
In addition, at least some known security detection systems include X-ray diffraction imaging (XDI) systems. At least some known XDI systems use inverse fan-beam geometry (a large source and a small detector) and a multi-focus X-ray source (MFXS). At least some known XDI systems provide an improved discrimination of materials, as compared to that provided by other known X-ray imaging systems, by measuring d-spacings between lattice planes of micro-crystals in materials. It is also known that X-ray diffraction may yield data from a molecular interference function that may be used to identify other materials, such as liquids, in a container. However, at least some known XDI systems generate an increased number of false positives due to a relatively low number of photons received at a detector element from a voxel of the container being scanned. In addition, while a number of photons received at a detector element may be increased by increasing an angular broadening of a scatter angle associated with the detector, such increased angular broadening results in an X-ray diffraction profile with increased measured peak widths of momentum transfer. Because narrower peak widths facilitate an identification of a scanned material, a disadvantageous result of angular broadening of the scatter angle to increase a number of photons received at a detector element is a corresponding decreased detection rate of a material.
To obtain the advantages of both multiview transmission imaging and XDI, at least some known security detection systems implement separate AT and XDI scanning systems. This increases both a size and a cost of the security detection system, and also increases a time needed to complete an investigation of each container.